CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION -

Transcription

1 CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION - Tatsunori YUHARA*, Kenichi RINOIE* and Yoshikazu MAKINO** *The University of Tokyo, Tokyo, , Japan **Japan Aerospace Exploration Agency, Tokyo, , Japan Abstract Next generation supersonic transports (SST) should have not only better aircraft performances but also less environmental impacts including sonic boom, emissions, and engine noise. With an increasing concern over the environmental and energy problems, alternative fuels have risen in significance. In this context, the authors have conducted a conceptual design study on LH 2 -fueled SST. In order to obtain a solution which has better aircraft performances and less environmental impacts, airframe and propulsion system integration is needed. By using our conceptual design environment, a global analysis on LH 2 -fueled SSTs has been conducted in comparison to kerosene SSTs. The result of the global analysis has shown that the optimum cruise altitude of LH 2 SSTs is higher than kerosene SSTs. In addition, one of the active constraints which determine the feasible design space is climb capability at cruise altitude. Then, suggestions have been made for improving the feasibility. 1 Introduction NASA announced stringent goals concerning what future SST systems should accomplish, including cruise efficiency, sonic boom, airport noise and NOx emission as shown in Fig 1.1.[1] In addition, it was reported by the IPCC that water vapor emissions in the stratosphere, where SSTs tend to fly, could have a significant impact on global warming.[2] With an increasing concern over the environmental impacts and energy problems, alternative fuels have risen in significance. Hydrogen-fueled aircraft were studied by NASA in the 1970s [3] and by EU in the 2000s [4]. The study conducted by NASA in the 1970s concluded that the LH 2 -fueled SSTs provided advantages in nearly every category including cost, sonic boom, airport noise, and emissions. One of the remarkable results is the 50% reduction in takeoff weight by the higher energy density. It should be noted that the 1970s were still a transition period of low sonic boom technology and climate change research work. Considering this background, the authors have conducted a conceptual design study on LH 2 -fueled SST. Our study started with the feasibility study which focused solely on airframe system.[5-6] After that, in order to evaluate the overall feasibility, the evaluation of propulsion system was added in our conceptual design environment.[7] Using the design environment, the aircraft performances and environmental impacts of LH 2 -fueled SSTs were assessed in comparison to kerosene fuel.[8] This paper will discuss the feasibility of LH 2 SSTs which is evaluated by considering aircraft performances and environmental impacts from the perspective of both airframe and propulsion system by conducting global analysis. 2 Conceptual Design Environment In general, conceptual design, which is performed in the upstream phase of aircraft design, often suffers from little available information. In order to fill the lack of information, the physics-based models are used in the aerodynamic and engine performance 1

2 Tatsunori YUHARA, Kenichi RINOIE, Yoshikazu MAKINO evaluation module, which are packaged in the conceptual design environment as shown in Fig A 3D panel code PANAIR [9] is utilized for the evaluation of aerodynamic performances including lift, pressure drag, moment, and near field signature. Viscous drag is obtained by a free source code FRICT [10]. These codes are selected for the speed and accuracy of conceptual design. A commercial code GasTurb [11] is used for the evaluation of engine performances including thrust, specific fuel consumption, jet velocity, and engine parameters (p3, T3, and T4). Among several aircraft performances in this study, the estimation of weight performance is the most difficult but critical performance. A conventional statistical approach is selected in this study.[12] The regression models of each weight components are constructed using the historical data of previous SST concepts.[13-16] After that, the regression models are modified using the weight data of Concorde.[17] Some additional components, such as tanks, have to be considered in the estimation of the weight of LH 2 SSTs, which will be explained in Section One of our main interests is to see how the requirements for environmental impacts affect the specifications of SSTs. The evaluation items in this study are sonic boom, airport noise, NOx emission, and water vapor emission (climate change impacts). The evaluation methods here have to be simple enough to be applicable in the conceptual design phase. In the sonic boom estimation, two methods are prepared. One is the first cut method by Carlson which outputs the pressure rise of sonic boom under the assumption of N-wave.[18] The other is a more accurate method which can consider the 3D shape of aircraft. The near-field signature is calculated using PANAIR while the far-field signature is obtained using the Thomas s method.[19-20] After that, the farfield signature is evaluated in PLdB. For the airport noise, only sideline noise is evaluated in this study using the following equation (1) which is derived from Ref.[21]. In general, the jet velocity is a determinant of the sideline noise of SSTs among the possible causes. (1) For the NOx emission, the following simplified equation (2) is utilized.[22] This equation requires the engine parameters of p3, T3, and T4. That is why GasTurb is utilized. (2) Water vapor mitigation was stated in the N+3 goals. This is because water vapor emissions in the stratosphere could have a significant impact on global warming according to the IPCC report. In addition, it is predicted that the emission altitude will also affect global warming because as emission altitude increases, the residence time of water vapor will extend. As IPCC cautioned, it is necessary to consider the global warming effect of SSTs. In this context, Grew developed a simplified global climate model, Climate Function, for the use of conceptual design of SSTs.[23] This model can predict future surface temperature change caused by SST fleet s emissions. The global warming due to water vapor emission is a non-negligible problem for LH 2 SSTs which will emit much more water vapor than conventional kerosene SSTs. Therefore, this study applies Climate Functions for the use of LH 2 SSTs with reasonable assumptions. This will be explained in Section The evaluation methods of environmental impacts were validated with the data of Concorde and Olympus 593. (not shown in this paper) 3 LH 2 SST 3.1 General Characteristics The fundamental differences between kerosene and hydrogen are compared in the Table. 3.1.[25] One of the notable differences is the energy density per unit weight of hydrogen which is 2

3 CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION - higher than that of kerosene. Accordingly, the necessary fuel weight of hydrogen aircraft for the same mission will be reduced by one-third. This is one of the outstanding advantages of hydrogen fuel. On the other hand, the energy density per unit volume of hydrogen is 0.25 times lower than that of kerosene. Accordingly, the necessary hydrogen fuel volume for the same mission will be increased by four times. The tank of hydrogen aircraft is different from that of kerosene aircraft in structure because of the chemical characteristics of hydrogen fuel. Hydrogen is liquefied at extremely low temperatures. In order to maintain its liquid state, the hydrogen tank requires a thermal insulation wall. Moreover, in order to prevent ambient air from entering into, the hydrogen tank has to be pressurized over 1.0 atm at least for ground operation, which is higher than the conventional cabin pressurization of 0.8 atm. Ideally, the hydrogen tank will have a cylindrical shape which receives the pressurization loading. Such a cylindrical tank will be installed not in the wing but in the fuselage. For these reasons above, a liquid hydrogen tank would be much heavier than that of kerosene tank. According to the study of hydrogen-fueled SST by NASA [3], the tank was conceptually designed at 21.5 K and 1.5 atm, which was estimated to be 24% of the fuel weight. Although the tank weight accounts for a relatively large portion of the total weight, the takeoff weight was reduced by 50% compared to the reference kerosene-fueled SST. This was due to the 75% reduction in the fuel weight. In the study of subsonic transport by EU [4], such a large takeoff weight reduction was not confirmed. Thus, one can say that, from the perspective of weight reduction, the application of hydrogen fuel is suitable for SST which stores a large amount of fuel. In the combustion room of engine, hydrogen fuel is burned in gaseous while kerosene fuel in liquid. Gaseous fuel can avoid the creation of local rich zones where NOx formation tends to occur. Furthermore, the flammable range of hydrogen is wider than that of kerosene so that the lean burn of hydrogen can be achievable. For these reasons, hydrogen aircraft will emit less NOx. However, the evaluation method of NOx emission in this study cannot take these phenomena into accounts. In addition, the combustion of hydrogen produces no CO 2 but 2.6 times more H 2 O per unit energy under the assumption of complete combustion. As mentioned in Chapter 1, water vapor emission which may lead to global warming is one of the concerns of SST. Although there are a lot of unknowns concerning the effects of water vapor emission at the stratosphere, the climate change impact should be considered in the application of hydrogen fuel. This study considers it by using Climate Function proposed by Grew. [23] 3.2 Basic Performances of LH 2 SST The engine and aerodynamic performances of LH 2 SST are evaluated in this study. In this evaluation, a pure turbojet was used for the comparison between kerosene and hydrogen fuel as shown in Table 3.2.[8] The jet velocity of a hydrogen engine was increased by 2.9% because the average molecular mass of emission gas was decreased, so that the speed of sound was also increased according to Eq. (3). The thrust was increased by 3.6% due to the increased jet velocity. The specific fuel consumption was reduced by 63.9% because of the slightly increased thrust and the markedly decreased fuel flow. (3) A conventional tube and wing geometry was used for the comparison of three different fuselage volume as shown in Fig [8] Among several performances, the difference in fuselage friction stood out more as shown in Fig [8] As mentioned in Section 3.1, one can expect that the advantage of a hydrogen-fueled aircraft would be expanded by increasing the amount of fuel. However, it results in larger fuselage volume and it is necessary to pay attention to the increment of fuselage friction drag. 3

4 Tatsunori YUHARA, Kenichi RINOIE, Yoshikazu MAKINO 4 Comparisons between LH 2 and Kerosene 4.1 Global Analysis Introduction In Chapter 3, the engine and aerodynamics performances of LH 2 SST are evaluated. In Section 4.1, the aircraft performances and the environmental impacts of LH 2 SSTs are evaluated in comparison with those of kerosene SST. The evaluations are made in a design space which is defined by nine design variables. In this paper, the authors analyzed the evaluation items (the aircraft performances and the environmental impacts) in the following methods. First, samples extracted from the above design space are analyzed by using Self- Organizing Map (SOM) [26] which is a datamining technique to classify the samples by similarity. This method can extract information about the relationships between design variables and evaluation items. Second, optimal solutions from the above design space are analyzed. The detail of the optimization will be explained later. In order to make a fair comparison between LH 2 SST and kerosene SST, preconditions are set carefully as shown in Table 4.1. The fuel weight and fuselage volume of the kerosene SST is given in reference to Concorde. Then, in order to give the same energy content to both the SSTs, the fuel weight of the LH 2 SST is determined. The additional components, fuel tank and supply system, are considered in the weight estimation in reference to the previous study of NASA [3]. The amount of the emission gas is also considered according to the composition (hydrogen: H 2, kerosene: C 12 H 23 ). The price of both fuels is given in order to evaluate direct operating cost (DOC). This study assumes that both fuels have the same fuel price per unit energy Analysis on the Relationships between Design Variables and Evaluation Items The analysis was performed using the same design space as the previous study [8], as shown in Table 4.2. In order to cover the entire range of the design space, 150 samples were extracted by using Latin Hypercube Sampling method. The nine evaluation items were monitored. The most interesting relationship is one between cruise altitude (ALT) and direct operating cost (DOC). For the SOM of kerosene SSTs, lower DOC solutions which are located at the upper left region have ALT of about 50kft as shown in Fig. 4.1 (a). On the other hand, for the case of LH 2 SSTs, lower DOC solutions have ALT of more than 56kft as shown in Fig. 4.1 (b). Behind this background is the fact that there is an optimal altitude which maximizes lift-drag ratio at a given wing loading as shown in Eq. (4-6). Eq. (5) shows the optimum lift coefficient which maximizes the lift drag ratio of Eq. (4). In order to attain the optimum lift coefficient of Eq. (5), one has to set a proper wing loading or a proper dynamic pressure as show in Eq. (6). (4) (5) (6) The reason for the difference in the optimum altitude between LH 2 SSTs and kerosene SSTs can be explained by the difference in the wing loading. LH 2 SSTs tend to have lower takeoff weight and larger wing area. The previous study [5-6] predicted the difference in the optimum altitude qualitatively. On the other hand, this study shows it quantitatively by using SOM Analysis on the Optimal Solutions It is necessary to run an optimization in selecting a better aircraft from a global design space. In this paper, the two design goals were adopted: minimizing DOC and minimizing climate change impact ( T). DOC is often used as a metric of aircraft. T was adopted as a goal since the specific target value of T has not yet been established. The same nine design 4

5 CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION - variables were used (see Table 4.2). The seven design constraints were given as shown in Table 4.3. Each constraint values were given with reasonable assumptions. This optimization utilized the optimization algorithm of NSGAII and the iteration was conducted until convergence. From Fig. 4.2 which shows the pareto solutions of both SST, one can see that the LH 2 SSTs tend to have larger T as expected. However, it is still possible to select a solution which has the same level of the T as the kerosene SST by sacrificing the DOC. From Table 4.4 which shows the specifications of pareto solutions of both SSTs, one can see that the takeoff weight of LH 2 SSTs is much less than that of kerosene SSTs while the wing area of LH 2 SST is much larger. Thus, LH 2 SSTs have lower wing loading. From Table 4.4, one can also see the difference in the active design constraints between LH 2 SSTs and kerosene SSTs. Although the design constraint of airport noise (NOISE) is active for both SSTs, that of the takeoff field length (TOFL) is active only for kerosene SSTs while that of climb capability at initial cruise altitude (ICAC) is active only for LH 2 SSTs. The reasons can be explained by the differences in the wing loading and optimum altitude. LH 2 SSTs have lower wing loading so that they can take off with a shorter TOFL. In addition, as the cruise altitude goes higher, the engine thrust decreases. Therefore, the requirement for ICAC will be strict for LH 2 SSTs. From Table 4.4, it is also found that the cruise speed of LH 2 SSTs was lowered. This is linked to the requirement for ICAC. In order to produce higher net thrust at cruise altitude, it is rational to reduce ram drag by lowering cruise speed. (Net thrust = gross thrust ram drag) 4.2 Sonic Boom Analysis Introduction In Section 4.1, the aircraft performances and the environmental impacts of LH 2 SSTs were analyzed in a global design space. In Section 4.2, the sonic boom of LH 2 SSTs was analyzed in detail by using a more accurate method (see Chapter 2). First, in order to establish a reference model, an airframe shape optimization was performed. Next, by using the reference model, the sonic boom of LH 2 SSTs was analyzed in comparison to that of kerosene SSTs Airframe Shape Design The six design variables of fuselage radius NURBS control points and wing planform parameters were used as shown in Fig The design goal is to minimize the sonic boom loudness (PLdB). The base model is the min. DOC solution of LH 2 SST (see Table 4.4). By optimizing the design variables manually, a low boom design was obtained and designated as a reference model Analysis on the Reference Models Sonic booms are affected by the altitude, speed, weight, and length of aircraft. The lower mass density and higher energy density of LH 2 make a difference in aircraft's size and weight. The effects of these differences on the sonic boom's loudness were compared. The airframe of both SSTs was based on the same reference model. The airframe shape of the kerosene SST was shrunk according to fuselage volume. It is found in Section that LH 2 SSTs have lower wing loading. According to Eq. (6), the lowered wing loading decreases the dynamic pressure if the lift coefficient is constant. The dynamic pressure is decreased by increasing altitude. Our motivation is to see how much the difference in altitude will have effects on sonic boom loudness. From Fig. 4.4 which compares the signatures at the same lift coefficient of 0.1, it is found that LH 2 SSTs can fly higher so that the sonic boom is quieter by 2.2 PLdB due to the altitude decay effect. The results are summarized in Table NOx Emission and Airport Noise 5

6 Tatsunori YUHARA, Kenichi RINOIE, Yoshikazu MAKINO Introduction In Section 4.1, the NOx emission and airport noise was evaluated in a simple way. In Section 4.3, those are discussed in detail NOx Emission It is expected that LH 2 engines will emit less NOx emission than kerosense engines for two reasons: gaseous combustion and wide flammability range. Gaseous combustion can make the temperature distribution of combustion room be uniform. With wide flammability range, lean combustion can be achieved. In the previous paper [8], the authors showed that flame temperature at the primary combustion zone can be reduced by 600 to 1500R. In order to exploit the favorable characteristics of H 2 combustor, the combustor needs to be re-designed compared with the conventional designs using regular diffusive combustion. One of the potential candidates is the micromix combustor.[27] Airport Noise In Section 4.1, only the sideline noise was evaluated. In FAR36, the airport noise of aircraft is evaluated at 3 measurement points: sideline, approach and cutback. In the previous paper [8], the authors showed the sideline noise of LH 2 SSTs will be increased by 1.3 EPNdB because the jet velocity of LH 2 SSTs increases. It is expected that conventional SSTs climb much more slowly than subsonic transports, so its cutback noise will be much louder. However, LH 2 SSTs will reduce cutback noise because of its shorter TOFL performance. 5 Feasibility of LH 2 SST In Chapter 5, the feasibility of LH 2 SSTs is discussed on the basis of the results of Section As discussed in Section 4.1, it is found that the active constraints of LH 2 SSTs are the airport noise requirement (NOISE) and the climb capability requirement at initial cruise altitude (ICAC). There are two methods to improve the ICAC performance: one is to reduce the cruise speed for reducing ram drag and the other is to change engine cycle for cruise condition. The former is a practical solution. For the latter, new propulsion technology needs to be developed such as a variable cycle engine. Furthermore, it is found that LH 2 SSTs tend to have larger global warming effect ( T). However, it is still possible to select a solution which has the same level of the T as the kerosene SSTs by sacrificing the DOC. As discussed in Section 4.2, the sonic boom of LH 2 SSTs will be reduced by about 2 PLdB due to the altitude decay effect. However, it is required to reduce the sonic boom more. Therefore, low boom technologies as to airframe need to be developed as ever. As discussed in Section 4.3, the NOx emission of LH 2 SSTs will be reduced significantly if a combustor for H 2 can be developed. As for the airport noise, the sideline noise will be increased by about 1 EPNdB because the jet velocity of LH 2 SSTs increases. On the other hand, the cutback noise will be reduced because LH 2 SSTs can take off more shortly so that the noise level will be reduced according to the distance between the measurement point and the source of noise. Since the cutback and approach noise are yet to be analyzed quantitatively in this study, these items should be considered in the future. It is necessary to continue to study alternative fuels for not only subsonic jets but also SSTs. Among them, LH 2 SSTs have outstanding features in takeoff weight and takeoff performances (TOFL and SSC). However, there still remain challenges to be solved. These challenges, mainly as to environmental impacts, should be tackled from the perspectives of both airframe and propulsion. 6 Conclusions In this paper, a global analysis on LH 2 -fueled SSTs was conducted in comparison to kerosene SSTs. Then, key technologies for improving the feasibility were discussed. 6

7 CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION - In Chapter 2, our conceptual design environment which was developed for the airframe and propulsion integration was shown. In Chapter 3, the general characteristics of LH 2 aircraft were discussed including fuel, tank, combustion, and emission. Then, the basic performances of LH 2 SSTs as to engine and aerodynamic were also discussed. One of the notable features is that from the perspective of weight reduction, hydrogen fuel which has higher energy density than kerosene fuel is suitable for SSTs which stores a large amount of fuel. In Chapter 4, the aircraft performances and the environmental impact of both SSTs were also evaluated. In the global analysis, the relationship between design variables and evaluation items were analyzed. The result of Self-Organizing Map showed that the altitudes for minimizing direct operating cost of both SSTs are different. In particular, the optimum cruise altitude of LH 2 SSTs will be higher than that of kerosene SSTs. In addition, the result of multi-objective optimization showed several important differences. Among them, the authors revealed the active constrains of LH 2 SSTs and kerosene SSTs: airport noise and climb capability at cruise altitude for LH 2 SSTs and airport noise and takeoff field length for kerosene SSTs. Furthermore, the environmental impacts of LH 2 SSTs were discussed including sonic boom, airport noise and NOx emission. In Chapter 5, the feasibility of LH 2 SSTs was discussed. Methods to improve cruise altitude climb capability which will be an active constraint for LH 2 SSTs were suggested. In addition, suggestions were made for improving other performances including climate change impact, sonic boom, airport noise and NOx emission. References [1] Coen, P., "Fundamental Aeronautics Program Supersonics Project," 5th Fundamental Aeronautics Program Technical Conference, [2] IPCC, "Aviation and the Global Atmosphere," [25 February 2013], [3] Brewer, G. D., "Final Report Advanced Supersonic Technology Concept Study- Hydrogen Fueled Configuration," NASA CR , [4] Westenberger, A., "Hydrogen Fuelled Aircraft," AIAA , [5] Yuhara, T. and Rinoie, K., "Conceptual Design Study on LH2 Fueled Supersonic Transport for Time Frame," AIAA , [6] Yuhara, T. and Rinoie, K., "Conceptual Design Study on Low Boom LH2 Supersonic Transport - Considering Climate Change Impact -," ICAS , [7] Yuhara, T., Rinoie, K., and Makino, Y., "Development of Airframe/Propulsion Integrated MDAO Environment for Conceptual Design of Supersonic Transport," 2013 Asia-Pacific International Symposium on Aerospace Technology, APISAT , [8] Yuhara, T., Rinoie, K., and Makino, Y., "Conceptual Design Study on LH2 Fueled Supersonic Transport considering Performance and Environmental Impacts," AIAA , [9] PDAS, [30 Octobar 2013]. [10] Mason, W. H., "Software for Aerodynamics and Aircraft Design," mason/masonf/mrsoft.html [30 Octobar 2013]. [11] Kurzke, J., GasTurb 12, [12] Glatt, C., "WAATS: A Computer Program for Weights Analysis of Advanced Transportation Systems," NASA CR-2420, [13] Mascitti, V., "A preliminary study of the performance and characteristics of a supersonic executive aircraft," NASA TM-74055, [14] Mack, R., "A supersonic business-jet concept designed for low sonic boom," NASA TM , [15] Fenbert, J., "Concept development of a Mach 2.4 high-speed civil transport," NASA TP , [16] Robins, A. and Dollyhigh, S., "Concept development of a Mach 3.0 high-speed civil transport," NASA TM-4058, [17] Nangia, R., Palmer, M., and Iwanski, K., "Towards Design of Long-range Supersonic Military Aircraft," AIAA , [18] Carlson, H. W., "Review of Sonic-Boom Generation Theory and Prediction Methods," The Journal of the Acoustical Society of America, Vol. 51, No. 2c, 1972, pp [19] Thomas, C., "Extrapolation of sonic boom pressure signatures by the waveform parameter method," NASA TN D-6832, [20] Makino, Y. and Makimoto, T., "Development of CAPAS, Conceptual Design Tool for Supersonic Aircraft," JAXA-SP , 2008 (in Japanese). [21] Stone, J., "Conventional profile coaxial jet noise prediction," AIAA Journal,

8 Tatsunori YUHARA, Kenichi RINOIE, Yoshikazu MAKINO [22] Morgenstern, J., Norstrud, N., Stelmack, M., and Stoch, C., "Final Report for the Advanced Concept Studies for Supersonic Commercial Transports Entering Service in the 2030 to 2035 Period, N+ 3 Supersonic Program," NASA CR , [23] Grewe, V., Stenke, A., Plohr, M., and Korovkin, V., "Climate functions for the use in multi-disciplinary optimisation in the pre-design of supersonic business jet," Aeronautical Journal, No. 3414, [24] Yuhara, T., Rinoie, K., and Makino, Y., "Conceptual Design Study on LH2 Fueled Supersonic Transport Incorporating Airframe/Propulsion Integrated MDAO Environment," JSASS 51st Aircraft Symposium 3B05, 2013 (in Japanese). [25] Hydrogen Fueled Aircraft Investigation Committees, "Current status of R & D on hydrogen fueled aircraft: A review," JAXA-SP , 2008 (in Japanese). [26] Kohonen, T., Self-Organizing Maps, Springer, [27] Svensson, F., "Potential of reducing the environmental impact of civil subsonic aviation by using liquid hydrogen," Ph.D. Thesis, Cranfield University, [28] Orlebar, C., The Concorde Story (sixth edition), Osprey publishing, [29] Morgenstern, J., Norstrud, N., Stelmack, M., and Stoch, C., "Final Report for the Advanced Concept Studies for Supersonic Commercial Transports Entering Service in the 2030 to 2035 Period, N+ 3 Supersonic Program," NASA CR , [30] Fahey, D., Keim, E., Boering, K., and Brock, C., "Emission measurements of the Concorde supersonic aircraft in the lower stratosphere," Science, Vol. 270, October, 1995, pp [31] Oishi, T., Tsuchiya, N., Nakamura, Y., Kodama, H., and Kato, M., "Research on Noise Reduction Technology," Ishikawajima-Harima engineering review, Vol.44, No.4, July, (In Japanese) Contact Author Address mailto: yuhara.tatsunori@jaxa.jp Copyright Statement The authors confirm that they, and/or their company or organization, hold copyright on all of the original material included in this paper. The authors also confirm that they have obtained permission, from the copyright holder of any third party material included in this paper, to publish it as part of their paper. The authors confirm that they give permission, or have obtained permission from the copyright holder of this paper, for the publication and distribution of this paper as part of the ICAS 2014 proceedings or as individual off-prints from the proceedings. Table 3.1 Fuel Property [25] Liquid Gaseous Hydrogen Jet A Composition H 2 C 12 H 23 Molecular mass Energy density kj/g Mass density kg/m Specific heat kj/kg/k Boiling temp. K Melting temp. K Vaporization heat J/g Cooling power kj/g > Flammable range % Ignition energy mj Table 3.2 Engine Performance [8] Kerosene LH 2 Altitude ft Speed M mass flow lb/s TIT R OPR p3 psia T3 R Fuel flow lb/s FN lb SFC lb/lb/hr Vj ft/s

9 CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION - Table 4.1 Preconditions for Designing SSTs (See the fourth paragraph of Section for more detail ) Kerosene Hydrogen Fuel capacity klb Fuselage Volume kft Tank weight lb W FUEL Fuel supply system weight Water vapor emission CO 2 emission Fuel price Table 4.2 Design Variables for Global Analysis Lower Upper Altitude kft Speed Mach FN lb BPR CPR TIT R Wing area kft 2 3.0(6.0)* 1 5.0(10.0)* 1 L.E. sweep angle deg T.E. sweep angle deg * 1 Values in the parenthesis is for LH 2 SSTs Table 4.3 Design Constraints for Global Analysis Limit Comment SSC - > 0.03 Minimal takeoff climb capability (FAR25) TOFL ft < Typical takeoff distance of international airport ICAC ft/s > 0 Minimal cruise climb capability RANGE nm > 3500 Range performance (Concorde: 4000nm)[28] ΔP psf < 2.25 Pressure rise of sonic boom (Concorde: 2.00psf)[29] EINOx g/kg < 15 NOx emission (Concorde: 23g/kg)[30] EPNL EPNdB < 100 Sideline noise level (Concorde: 120EPNdB)[31] Table 4.4 Optimums extracted from Pareto Solutions Kerosene SSTs LH 2 SSTs Min. ΔT Min. DOC Min. ΔT Min. DOC Comment Altitude [ft] Higher altitude Speed [-] Lowered speed FN [lb] BPR [-] CPR [-] TIT [R] Wing area [ft 2 ] Enlarged wing area L.E. sweep angle [deg] T.E. sweep angle [deg] RANGE [nm] ICAC [ft/s] Active constraint for LH2 SSTs TOFL [ft] Active constraint for kero. SSTs SSC [-] NOISE [EPNdB] Active constraint for both SSTs EINOx [lb/klb] ΔP [psf] Max. takeoff weight [lb] Weight reduction Empty weight [lb] Fuel weight [lb]

10 Tatsunori YUHARA, Kenichi RINOIE, Yoshikazu MAKINO Table 4.5 Summary of Sonic Boom Analysis Kerosene LH 2 Comment Speed Mach Altitude ft Cruise weight lb % fuel consumed Length ft Wing area ft Wing loading (W/S) lb/ft CL Sonic boom loudness PLdB Airframe 320 ft 239 ft Fig.1.1 NASA N+3 Target [1] Fig. 2.1 Conceptual Design Environment [7-8] Fig. 3.1 LH2 SSTs with Different Fuselage Volumes (30k, 40k, 50kft 3 ) [8] Fig. 3.2 Drag Components (30k, 40k, 50kft 3 ) [8] 10

11 CONCEPTUAL DESIGN STUDY ON LH 2 FUELED SST - ENVIRONMENTAL IMPACTS REDUCED BY AIRFRAME/PROPULSION SYSTEM INTEGRATION - (a) Kerosene SSTs (b) LH 2 SSTs Fig. 4.1 SOM as to Cruise Altitude (ALT) and Direct Operating Cost (DOC) Fig. 4.3 Design Variables for Sonic Boom Analysis (Airframe Shape Design) Fig. 4.2 Pareto Solutions [8] (See also Table 4.3) Fig. 4.4 Sonic Boom Signatures [8] (See also Table 4.4) 11